2001 Mazda 626 P0421 Catalyst Code

MAZDA 626
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IRISH81449
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I have a Mazda 626.2001 4 cyl. auto. 76K. Check engine light came on. Autozone checked and code P0421 came on. The counter guy suggested a tune-up. I had one in March. Maybe 5K on car since then. The read out states warm-up catalyst efficiency for bank 1 is below threshold. What does that mean and where do I go from here.? Thanks
Bill from ohio
Oct 20, 2006 at 4:14 AM
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COSMO
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Hi Irish,

Well there are a few things that could be going wrong.....

1. The front cat (right under the manifold) might be bad....this can be diagnosed by check the front and rear 02 sensors the see if they are switching at the same rate (ie the cat is bad).

2. There might be a PCM update for this code, but if left too long you might need to replace both the front cat and have the pcm updated.

So my sudgestion is to see a Mazda dealer for this code.

Cosmo

Mazda Tech
Oct 20, 2006 at 12:21 PM
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IRISH81449
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I have been told that Mazda has a 8yr. 80K warranty on their emissions. Is this true ?? I have reseached and only find said warranty on Miata model.
Bill
Oct 20, 2006 at 1:22 PM
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COSMO
  • ✓Experienced Mechanic
  • 347 POSTS
Well that depends on where you are....I am in Canada, here Mazda has a 3 year 80k warrenty on bumper to bumper warrenty, thern a 5 year 100km on their powertrain.

There is however a 7year 128,000km warrenty on some emmision components ie: cats and PCM's (but don't quote me). The bestthing to do is get in contact with your local Mazda dealer. Taking a detailed vehicle repair history with you would be an asset to you at the time of diagnosis as well.

Cosmo

Mazda Tech
Oct 20, 2006 at 2:19 PM

Suggested Repair

Have a Mazda dealer diagnose P0421. Compare front and rear oxygen-sensor switching to check whether the front catalytic converter is inefficient, and ask about a PCM update and emissions-warranty coverage. Bring the repair history; if the fault is left too long, both the front converter and a PCM update may be needed.

Conversation Summary

A 2001 Mazda 626 with 76,000 miles set code P0421, warm-up catalyst efficiency below threshold for bank 1, shortly after a tune-up. The Mazda technician said the front catalytic converter may be failing and can be checked by comparing front and rear oxygen-sensor switching rates. A PCM update may also apply, and delaying repair could require both the converter and the update. The owner asked about an 8-year/80,000-mile emissions warranty; the technician said coverage depends on location and advised contacting a local Mazda dealer with a detailed repair history.

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